Proton conductive polymers, such as the sulfonated fluoropolymer NAFION®, have been used as solid ion exchange membrane materials in fuel cells. Although such membrane materials work reasonably well, demanding fuel cell applications, such as automotive fuel cells, require significant improvements. In such fuel cell applications, fuel cells require a large current density in a wide range of operating conditions for a long product life cycle. The membrane in those fuel cells must have high proton conductivity and minimal dimension change in a wide range of humidity and temperatures. Many random copolymers may provide high proton conductivity if sufficient hydration level and high ion exchange capacity are achieved. At high hydration level and high relative humidity, however, excessive membrane swelling cannot be avoided with random copolymers. It is difficult for random copolymers to provide high proton conductivity and excellent mechanical stability simultaneously under a wide range of fuel cell operating conditions. Certain types of block copolymers have been disclosed as improvement over random copolymers due to their ability to form different morphologies with interconnected hydrophobic domains and proton conductive domains. It is conceivable that some of the block copolymers might provide both high proton conductivity and mechanical stability in a wide range of fuel cell operation conditions. When a block copolymer is processed into a membrane, however, the block copolymer doesn't spontaneously form the most desirable morphology to afford the membrane properties required for optimal fuel cell operation. Besides, the most desirable morphology has not been taught or disclosed.
Accordingly, there is a need for improved methods of making ion conducting membranes.